1. Field of the Invention
This invention relates to a system and method for preventing biological contamination of a semi-permeable membrane in a reverse osmosis system.
2. Background Information
Reverse osmosis systems are used to purify water by supplying a pressurized feed water stream to one side of a semi-permeable membrane in a reverse osmosis device. The pressure is maintained at a level sufficient to force the water through the membrane while retaining dissolved impurities on the feed water side. One important application is the purification of water used for human consumption. Purification removes impurities which make the water unsafe or unpotable, or which impart an undesirable taste or appearance to the water.
The treatment of water that contains microorganisms can limit the useful life of the semi-permeable membrane. The microorganisms tend to become imbedded and multiply in the membranes, causing clogging and fouling of the reverse osmosis unit. Further, the multiplying presence of the microorganisms increases the adverse consequences of their presence in the feed water. Treatment of water to combat microorganisms reduces the presence and effect of the microorganisms in proportion to the number of organisms present. Therefore, the multiplying of microorganisms on the semi-permeable membrane reduces the purity of product water from the reverse osmosis device and requires more aggressive measures to kill the microorganisms in the product water.
Large municipal and industrial reverse osmosis systems utilize out of system scrubbing of the semi-permeable membranes, careful chemical treatment of the feed water, and/or special chemical flushing cycles to control the buildup of microorganisms and other impurities on the semi-permeable membrane. However, such techniques are impractical for small point of use systems, such as under-sink home units, which must be small, simple, and reliable. These systems should require infrequent servicing and preferably be operable without electric power. Typically these systems will operate to purify water during and following the dispensing of water from the system and then shut down for period of hours or even days. During the shut down period the feed water is stagnant against the semi-permeable membrane, providing conditions that are conducive to multiplication of microorganisms present in the feed water.
Accordingly, there is a need for a simple and reliable device to prevent biological contamination of the semi-permeable membrane in a reverse osmosis device.